Nine waterspouts formed on Lake Michigan on Saturday and forecasters say the conditions could trigger more on Sunday.
Boaters should be on alert for these 'tornadoes over water'.
The spouts form when there's moist, warm environment near the surface of a lake.
When cold air over-rides the surface conditions, it creates funnel clouds.
Usually only a small environment - typically about a kilometre or so - is affected.
Waterspouts are viewed from a safe distance, because winds around them can be as high as 100 km/h.